A liquid crystal display device is a display device with low electrical power consumption and it can be lightened and thinned. Therefore, the liquid crystal display device has been widely used in a TV, a monitor for personal computers, a monitor for personal digital assistances, and the like. The liquid crystal display device which has been commonly used currently has a configuration in which liquid crystal is interposed between two glass substrates including electrodes and for sealing, a sealant is arranged at the edge of the both substrates. Plastic beads uniform in particle size are scattered as a spacer between the two substrates, and thereby a space between the two substrates is kept at a certain distance.
According to a liquid crystal display device for color display (color liquid crystal display device), on one of the above-mentioned two glass substrates, a color filter layer including colored parts of red (R), green (G), and blue (B), and a shielding layer (BM: BlackMatrix) partitioning the colored parts of R, G, and B is formed. Further, an active matrix driving color liquid crystal display device generally includes a TFT array substrate that is an active matrix substrate and an opposite substrate arranged to face the TFT array substrate. The TFT array substrate generally includes: a switching element such as a thin film transistor (TFT) including a semiconductor layer made of amorphous silicon (a-Si), polysilicon (p-Si) and the like; and a pixel electrode, a source bus line, and a gate bus line, each connected to the switching element. The opposite substrate generally includes an opposite electrode and a color filter layer. Then, a polarizer is arranged on each main surface of the both substrates in this display device. As a result, such a display device can display color images.
Examples of liquid crystal mode of the liquid crystal display device include TN (Twisted Nematic) mode, STN (Super Twisted Nematic) mode, GH (Guest Host) mode, ECB (Electrically Controlled Birefringence) mode, FLC (Ferroelectric Liquid Crystal) mode. In each mode, it is advantageous in terms of production of the display device that the color filter layer is arranged on the opposite substrate having a relatively simple electrode configuration. However, the opposite substrate and the active matrix substrate might be misaligned at the time of attachment. Therefore, the BM needs to have an opening smaller than an opening formed on the active matrix substrate. As a result, an aperture ratio is decreased.
In addition, a pixel needs to have a high aperture ratio in order to improve a luminance in the liquid crystal display device. In order to improve the aperture ratio of the pixel, a technology for providing a production facility which permits higher-precision alignment has been developed. However, according to a current production method, the improvement in aperture ratio, attributed to the improvement in alignment technology, is difficult.
A Color-filter on array (COA) structure in which a color filter layer is formed on an active matrix substrate has been currently developed. This structure needs no alignment at the time when an active matrix substrate including a color filter layer (COA substrate) is attached to an opposite substrate including an electrode over the entire surface thereof. Therefore, no misalignment defect in the attachment step is generated. Further, the production steps can be simplified as the alignment process is not needed. In addition, a problem in alignment accuracy at the time when the both substrates are attached to each other is not generated. Therefore, a pattern can be designed without taking the misalignment into consideration, and a BM pattern is formed to have a smaller width. As a result, the aperture ratio can be highly increased.
Various methods such as a staining method, a pigment dispersion method, an electrodeposition process, and a film transfer method have been developed as a method of forming the color filter having the COA structure. According to a conventional COA structure, the respective colored parts of R, G, and B are formed in a layer between a switching element formed on the lower layer side and a pixel electrode formed on the upper layer side. Therefore, a contact hole is formed in the respective colored parts, and thereby the pixel electrode needs to be conducted to the switching element through this contact hole. Accordingly, if this color-filter on array structure is formed by the production method of the color filter, how to form the contact hole in the respective colored parts is important.
A method of producing the colored parts of the color filter layer with an ink-jet apparatus (hereinafter, also referred to as an “ink-jet method”) has been actively developed. This method has advantages such as simple production processes and low production costs. However, formation of the COA structure using the ink-jet method has a problem in how to form the above-mentioned contact hole. That is, no photomask is used in the ink-jet method, and therefore, the colored parts of R, G, and B are generally made of a material without photosensitivity. Hence, a photolithography process can not be used to form a contact hole in the color filter layer.
Under such a circumstance, the following methods have been proposed. A method of forming a through-hole in a switching element region of a light-shielding layer (for example, refer to Patent Document 1); and a method of providing an opening of a partition (also serving as an BM) with a projection, and inhibiting an ink from intruding into the projection by utilizing a surface tension of the ink, thereby using this projection as a contact hole (for example, refer to Patent Document 2). However, according to these methods, a BM-remaining part and a BM-removed part exist on a line joining one opening to another opening through the contact hole. As a result, the BM pattern needs to have a certain width, and therefore, the high aperture ratio, which is a merit of the COA structure, can not be provided. According to the method utilizing the surface tension of the ink, the ink intrusion might not be sufficiently suppressed depending on a material for the ink, and a connection defect between the switching element and the pixel electrode is generated in certain instances. Thus, there is room for improvement in these conventional technologies in order to improve the aperture ratio and suppress the generation of the connection defects.    [Patent Document 1]    Japanese Kokai Publication No. 2000-122072    [Patent Document 2]    Japanese Kokai Publication No. 2002-131735